Organic Transport Layers Research Articles

Approaching the fill factor Shockley–Queisser limit in stable, dopant-free triple cation perovskite solar cells

High fill factor, large area perovskite solar cells are realized with undoped organic transport layers by optimizing the charge carrier transit through PTAA.

Improved air stability of perovskite solar cells via solution-processed metal oxide transport layers.

Lead halide perovskite solar cells have recently attracted tremendous attention because of their excellent photovoltaic efficiencies. However, the poor stability of both the perovskite material and the charge transport layers has so far prevented the fabrication of devices that can withstand sustained operation under normal conditions. Here, we report a solution-processed lead halide perovskite solar cell that has p-type NiO(x) and n-type ZnO nanoparticles as hole and electron transport layers, respectively, and shows improved stability against water and oxygen degradation when compared with devices with organic charge transport layers. Our cells have a p-i-n structure (glass/indium tin oxide/NiO(x)/perovskite/ZnO/Al), in which the ZnO layer isolates the perovskite and Al layers, thus preventing degradation. After 60 days storage in air at room temperature, our all-metal-oxide devices retain about 90% of their original efficiency, unlike control devices made with organic transport layers, which undergo a complete degradation after just 5 days. The initial power conversion efficiency of our devices is 14.6 ± 1.5%, with an uncertified maximum value of 16.1%.

Direct Electrical Evidence of Plasmonic Near-Field Enhancement in Small Molecule Organic Solar Cells

We present a simple and versatile technique to introduce plasmonic silver nanoparticles into organic thin film devices by in situ vacuum deposition. Silver particles with 80 nm diameter at the back of small molecule organic solar cells increase the power conversion efficiency (PCE). Doped organic transport layers allow one to separate electrical and optical effects. By a systematic variation of the position of the silver particles within the solar cell stack, we can thus clearly distinguish a near-field photocurrent gain in the IR that decays to one-half on length scales of around 4 nm, and a less distance-dependent selective mirror effect for short wavelength, which allows one to optimize devices for different wavelengths simultaneously. Device optimization reveals that plasmonic increased absorption can be used to significantly reduce the thickness of the absorber layers and gain efficiency through improved transport properties. A plasmonic zinc phthalocyanine fullerene-C60 solar cell that yields improv...

Visible Colloidal Nanocrystal Silicon Light-Emitting Diode

We herein demonstrate visible electroluminescence from colloidal silicon in the form of a hybrid silicon quantum dot-organic light emitting diode. The silicon quantum dot emission arises from quantum confinement, and thus nanocrystal size tunable visible electroluminescence from our devices is highlighted. An external quantum efficiency of 0.7% was obtained at a drive voltage where device electroluminescence is dominated by silicon quantum dot emission. The characteristics of our devices depend strongly on the organic transport layers employed as well as on the choice of solvent from which the Si quantum dots are cast.

Cheap <italic>p</italic>- and <italic>n</italic>-doping for highly efficient organic devices

Electrically doped, organic transport layers are important for today's high efficiency organic (opto-)electronic devices. Doped organic layers have a strongly increased free charge carrier density compared to their undoped counterparts and also improve the charge carrier injection from adjacent electrodes into the organics. For practical applications, especially in optoelectronics, these layers have to have low absorption in the wavelength range of interest. The two nearly colorless p - and n -doping materials, rhenium heptoxide and cesium carbonate, are investigated focusing on their conductivity enhancement, injection improvement, and voltage drop over doped transport layers in organic light emitting diodes. They show very good doping properties already at moderate doping concentrations and prove that they can be used in variable thicknesses without a significant voltage increase. This makes them cheap, low absorbing alternatives to today's, well-established doping systems.

High-efficiency broadband solar cell architectures based on arrays of volumetrically distributed narrowband photovoltaic fibers

We propose a novel solar cell architecture consisting of multiple fiber-based photovoltaic (PV) cells. Each PV fiber element is designed to maximize the power conversion efficiency within a narrow band of the incident solar spectrum, while reflecting other spectral components through the use of optical microcavity effects and distributed Bragg reflector (DBR) coatings. Combining PV fibers with complementary absorption and reflection characteristics into volume-filling arrays enables spectrally tuned modules having an effective dispersion element intrinsic to the architecture, resulting in high external quantum efficiency over the incident spectrum. While this new reflective tandem architecture is not limited to one particular material system, here we apply the concept to organic PV (OPV) cells that use a metal-organic-metal-dielectric layer structure, and calculate the expected performance of such arrays. Using realistic material properties for organic absorbers, transport layers, metallic electrodes, and DBR coatings, 17% power conversion efficiency can be reached.

A Color‐Tuneable Organic Light‐Emitting Transistor

An organic light-emitting field-effect transistor whose emission color can be changed by the applied voltage is presented. The transistor is based on a parallel layer stack of acenes serving as organic transport and emission layers. During operation, the position of the recombination zone can be moved by a proper change in the drain and gate bias from one organic semiconductor of the stack to the other, inducing a change in the emission color from green to red.

On the role of spin polarization of electrons in the effect of giant injection magnetoresistance in the Ni-polymer-Cu system

The effect of spin polarization of electrons injected from a ferromagnet on the giant injection magnetoresistance was investigated for a ferromagnet-polymer-nonmagnetic metal experimental structure. The degree of spin polarization was varied by introducing a depolarizing nonmagnetic metal (Cu) layer between the ferromagnet and the organic transport layer. It was established that the coefficient of giant injection magnetoresistance depends significantly on the thickness of the depolarizing layer. In particular, the effect was not observed at a thickness larger than 12 nm and decreased exponentially at a smaller thickness as the thickness increased. The conclusion was drawn that the spin polarization of electrons plays a decisive role in the effect of giant injection magnetoresistance.

Control of carrier transport in organic semiconductors by aluminum doping

Control of carrier transport in organic semiconductors by aluminum doping is realized in organic light-emitting devices (OLEDs) for which electroluminescence can sensitively reflect the status of carrier transport. It is found that an Al-doped layer with proper thickness (∼1–10nm) may block hole transport completely and enhance electron transport to some extent regardless of its location in the organic carrier transport layers. Improvement in the efficiency of OLEDs with an aluminum cathode is achieved upon the introduction of a very thin (∼3nm) Al-doped region near the light-emitting area. The current efficiency obtained with such Al-doped devices is about 30% higher than that with undoped devices.

Electronic traps in organic transport layers

The knowledge about properties of electronic traps in organic semiconductors is one of the major keys for the understanding and optimization of charge transport in organic devices. In the present article the density of occupied states of the most prominent pristine small molecule systems and selected polymers are reported determined, by fractional thermally stimulated current and luminescence techniques. In order to distinguish between impurity and structurally based traps, model systems of doped as well as differently deposited layers were studied. In addition, the influence of detected traps on steady state I–V and dynamic time-of-flight characteristics are reported. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Covalently Interlinked Organic LED Transport Layers via Spin-Coating/Siloxane Condensation

Covalently Interlinked Organic LED Transport Layers via Spin-Coating/Siloxane Condensation

Confinement of charge carriers and molecular excitons within 5-nm-thick emitter layer in organic electroluminescent devices with a double heterostructure

Organic electroluminescent devices with a double-heterostructure indium-tin-oxide substrate/hole transport layer/emitter layer/electron transport layer/MgAg have been fabricated by vacuum vapor deposition. The organic carrier transport and emitter layers were composed of amorphous films. In the double-heterostructure devices, the luminance continued to lie in high level, even when the emitter thickness was 50 Å. The confinement of charge carriers and molecular excitons within a narrow emitter layer was achieved.